The present invention relates to methods and devices for controlling the kinetic energy and/or the efficiency of desorption of neutral molecules from a surface. The present invention relates to methods and devices for controlling the kinetic energy and/or the efficiency of desorption of neutral molecules from a surface Development of devices for desorption ionization of molecules direct from solids, and liquids in open air using a direct analysis in real time (DART) source has previously been described in US Pat. No. 6,949,741 “Atmospheric Pressure Ionization Source” which is expressly incorporated by reference in its entirety. DART uses a heated carrier gas to effect desorption of sample into that same carrier gas where gas phase ionization occurs. Unfortunately, the heating of the carrier gas to a sufficient temperature to enable desorption of some analytes takes considerable time. Further, the transfer of heat to the sample by that gas is not very efficient. A gas ion separator described in U.S. Pat. No. 7,700,913, “Sampling system for use with surface ionization spectroscopy” which is expressly incorporated by reference in its entirety can be used to improve the efficiency of sampling.